Question

New to scheme here. I’m trying to compile a scheme function, range. It’s very simple – it takes a start, step and stop list L and makes a new list where every element = stepAmt + curStep.

For example: (range ‘(0 2 7)) => (0 2 4 6), (range ‘(2 2 0)) => ()

When I try to compile

(define (helper2(start stepAmt stop curStep newList)
(if (> start stop)
    '()
    (if (> (+ stepAmt curStep) stop)
        newList
        (helper2 (start stepAmt stop (+ stepAmt curStep) (concat newList (+stepAmt curStep))))))))

I get the error

Ill-formed special form: (define helper2 (start stepamt stop curstep newlist) (if … … …))

I’m not sure what it means. I’ve double checked my logic and parentheses and can’t figure it out.

This is the function that will call that function:

(define (example L)
(let (
    (start (car L))
    (curStep (car (cdr L)))
    (step (car (cdr L)))
    (stop (car (cdr (cdr L))))
    )
    (helper2 (start step stop curStep '()))
)

)

Any pointers would be great. I’m not sure if it’s a typo or a logical error. Thank you!

Answer 1

You need not

(define helper2 (some arguments go here)
   definition goes here)

but

(define (helper2 some arguments go here)
  definition goes here)

The way to remember this is that what goes after define looks just like a call to the function you’re defining. “Here’s how to deal with a call like (helper2 some arguments go here): …”